1. Field of the Invention
The present invention relates to a drawing machine for drawing a plate-type workpiece, which is supported by a lower die, into a prescribed configuration with a drawing die.
2. Description of the Background Art
FIG. 15 is a sectional view showing a ventilator cover 1, which is an example of a product drawn by a drawing machine. This ventilator cover 1 has three-stage drawn parts 2, 3 and 4, as well as an opening 5 provided in its center.
The ventilator cover 1 is drawn into a prescribed configuration from a metal plate 6 shown in FIG. 16A. In this case, various problems are caused if the three-stage drawn parts 2, 3 and 4 are simultaneously formed in a single drawing step. For example, the workpiece, i.e., the metal plate 6 may be broken or creased. Therefore, such a plurality of stages of drawn parts are generally formed in the plate-type workpiece one by one from the first-stage drawn part.
FIGS. 16B to 16E sequentially illustrate steps which are generally employed for manufacturing the ventilator cover 1. The metal plate 6 shown in FIG. 16A is first drawn with an upper die 7 and a lower die 8, as shown in FIG. 16B. The first-stage drawn part 2 is formed in this step. Both the upper die 7 and the lower die 8 have configurations corresponding to the first-stage drawn part 2. The upper die 7 has a shearing blade in its center for forming the opening 5 in the metal plate 6 simultaneously with the first-stage drawn part 2.
The workpiece thus provided with the first-stage drawn part 2 is transferred to another press, which has an upper die 9 and a lower die 10 as shown in FIG. 16C, so that the second-stage drawn part 3 is drawn therein.
Then the workpiece is transferred to still another press, which has an upper die 11 and a lower die 12 as shown in FIG. 16D, so that the third-stage drawn part 4 is drawn therein. Finally the workpiece is transferred to a further press which has an upper die 14 and a lower die 15. The upper die 14 has a shearing blade 13, which cuts/removes an edge portion 16 of the workpiece. Thus, the ventilator cover 1 is obtained in the prescribed configuration shown in FIG. 15.
In order to form a drawn part having a specific pattern in a plate-type workpiece, it has generally been necessary to prepare an upper die and a lower die in correspondence to the pattern. Therefore, absolutely different types of upper and lower dies are required for changing the pattern of the drawn part. In order to form a drawn part having a triangular plane configuration after forming a drawn part having a quadrangular plane configuration by the same press, for example, it is necessary to demount an upper die and a lower die for the drawn part having the quadrangular pattern from the body of the press and to newly mount an upper die and a lower die for the drawn part having the triangular pattern. Such operation is complicated and takes much time for exchanging jigs and tools.
In order to successively form a plurality of stages of drawn parts in the metal plate 6 as shown in FIGS. 16B to 16E, further, different presses are required for the respective stages of drawn parts. Therefore, four presses are required for forming four-stage drawn parts in the metal plate, for example. Thus, the cost for the overall manufacturing facility is increased while the area required for installing the manufacturing facility is also increased.